It is known that chlorine is useful as a raw material of vinyl chloride, phosgene, etc., and can be produced by oxidizing hydrogen chloride. For example, the Deacon reaction using a Cu catalyst is well known. For example, a method for oxidizing hydrogen chloride with a catalyst containing a ruthenium compound is described in West German Patent No. 1,567,788 and, there is also described that ruthenium (III) chloride is particularly effective among the ruthenium compounds. Furthermore, a method for supporting a ruthenium compound on a carrier is also described and, as the carrier, silica gel, alumina, pumice stone and ceramic material are exemplified. As the Example, a ruthenium chloride catalyst supported on silica is exemplified. However, a test was conducted using a catalyst prepared by using a method for preparing a silica-supported ruthenium (III) chloride described in said patent. As a result, the ruthenium compound as a catalyst component is drastically volatilized and it was disadvantageous for industrial use. For example, a method for oxidizing hydrogen chloride with a chromium oxide catalyst is described in EP0184413 A2. However, a method which has hitherto been known had a problem that the activity of the catalyst is insufficient and high reaction temperature is required.
When the activity of the catalyst is low, it is necessary to make the reaction temperature higher but the reaction of oxidizing hydrogen chloride with oxygen to produce chlorine is an equilibrium reaction. When the reaction temperature is high, it becomes disadvantageous in view of equilibrium and the equilibrium conversion of hydrogen chloride becomes lower. Therefore, when the catalyst has high activity, the reaction temperature can be decreased and, therefore, the reaction becomes advantageous in view of equilibrium and higher conversion of hydrogen chloride can be achieved. In case of high temperature, the activity is lowered by volatilization of the catalyst component.
Both high activity and high activity per unit weight of ruthenium contained in the catalyst are required to the catalyst, industrially. Since high activity per unit weight of ruthenium contained in the catalyst can reduce the amount of ruthenium contained in the catalyst, it becomes advantageous in view of cost. It is possible to select the reaction condition which is more advantageous in view of equilibrium by conducting the reaction at a lower temperature using a catalyst having high activity. It is preferred to conduct the reaction at a lower temperature in view of stability of the catalyst.
In these points of view, the development of the catalyst which can be used at low temperature have been required.